One form of dry transfer material includes an adhesive layer applied to one surface of a permanent, continuous, self-supporting base film and one or more ink layers distributed in a graphic pattern on the opposing face of the base film. The fil provides a substrate for the ink and adhesive, and maintains the two permanently separated so as not to contaminate one with the other. Also, because of the relatively thick, self-supporting nature of the film, the transfer article is storable and handleable without substantially wrinkling, cracking, or the like. Along with the advantages conferred by the presence of the base film are certain disadvantages, principally cost of the film, and the substantial thickness its presence imparts to the transfer article. This latter feature creates both aesthetic and performance drawbacks. Aesthetically, the high profile of the transfer article relative to the surface of the substrate to which the article is affixed may create an artificial appearance. From a performance standpoint, the higher profile increases the likelihood that the transfer article will be lifted at the edges allowing foreign matter to invade the space between the substrate and the transfer article, causing further erosion of the adhesive bond. Reducing the base or support film thickness leads to a reduction in the advantages sought to be achieved by the film.
Another form of transfer article eliminates altogether the support or base film, providing a marking as thin as 10 to 40 microns. Such an article approximates painted markings in aesthetics. However, elimination of the base film imposes such substantial restrictions on both the manufacturing techniques required to construct such an article and the materials which can be utilized in the construction as to militate against adoption of this form for many uses, particularly where rigorous environmental conditions may be encountered. Among the manufacturing restrictions are the need to reverse print the graphic design (for two color printing, the second layer must be printed before the first ink layer) and the dependence upon selective techniques for applying the adhesive (silk screening or gravure printing rather than roll coating). In terms of material restrictions, a principle one is that the adhesive is generally a latent type, for example, a water-soluble or solvent activated adhesive. This in turn requires that an adhesive actuation step be introduced into the bonding procedure, adding additional time, difficulty, and skill demands to the use of this type of decal. Such support film-free graphics are also generally more brittle and less tough, restricting if not eliminating the type of cutting and trimming operations which are employed with conventional film-based graphics to provide the finished decal pattern and remove waste.
U.S. Pat. No. 4,454,179 (Bennett et al.) describes a dry transfer article that includes a carrier film bearing a graphic design in the form of a predetermined ink pattern. An actinic radiation-sensitive adhesive overlaps the ink pattern. The ink pattern acts as a mask to the radiation so that only adhesive in non-ink areas is exposed to radiation. This creates a differential adhesive tack which allows the transfer article to be positioned on a substrate and the carrier film and exposed adhesive selectively removed, leaving the graphic design and underlying unexposed adhesive bonded to the surface. This patent describes articles made by reverse printing. Additionally, it describes the direct application of the graphic to the carrier. Generally, only low adhesive forces hold the graphic to the carrier. This can lead to difficulty when the transfer article is subsequently positioned or repositioned on a substrate, as the graphic may release prematurely from the carrier.
U.S. Pat. No. 4,514,457 (Sasaki) describes a transfer article having an adhesive layer, a coating of particles on one surface of the adhesive layer which provides an ink-receptive surface, and a graphic image on the particle layer. A binder is preferably employed with the particle layer so as to prevent migration of adhesive through the particle layer into the graphic image layer. The adhesive employed is preferably a room temperature, pressure-sensitive adhesive, although a heat-sensitive adhesive may be used.